Aprotinin (also known as bovine pancreatic trypsin inhibitor, BPTI) is a basic protein present in several bovine organs and tissues, such as the lymph nodes, pancreas, lungs, parotid gland, spleen and liver. It is a single-chain polypeptide of 58 amino acid residues with the following amino acid sequence
Arg Pro Asp Phe Cys Leu Glu Pro Pro Tyr Thr Gly Pro Cys Lys Ala Arg Ile Ile Arg Tyr Phe Tyr Asn Ala Lys Ala Gly Leu Cys Gln Thr Phe Val Tyr Gly Gly Cys Arg Ala Lys Arg Asn Asn Phe Lys Ser Ala Glu Asp Cys Met Arg Thr Cys Gly Gly Ala (SEQ ID NO:1). PA0 X.sub.1 -Asp-Phe-Cys-Leu-Glu-Pro-Pro-Tyr-Thr-X.sub.2 -X.sub.3 -X.sub.4 -X.sub.5 -X.sub.6 -X.sub.7 - X.sub.8 -X.sub.9 -Arg-Tyr-Phe-Tyr-Asn-Ala-Lys-Ala-Gly-Leu-Cys-Gln-Thr-Phe-Val-Tyr-Gly-Gly-X .sub.10 -Arg-Ala-X.sub.10 -Arg-Ala-X.sub.11 -X.sub.12 -Asn-Asn-Phe-Lys-Ser-Ala-Glu-Asp-Cys-Met-Arg-Thr-Cys-Gly-Gly-Ala (I) PA0 X.sub.1 -Asp-Phe-Cys-Leu-Glu-Pro-Pro-Tyr-Thr-X.sub.2 -X.sub.3 -X.sub.4 -X.sub.5 -X.sub.6 -X.sub.7 -X.sub.8 -X.sub.9 -Arg-Tyr-Phe-Tyr-Asn-Ala-Lys-Ala-Gly-Leu-Cys-GIn-Thr-Phe-Val-Tyr-Gly-Gly-X .sub.10 -Arg-Ala-X.sub.11 -X.sub.12 -Asn-Asn-Phe-Lys-Ser-Ala-Glu-Asp-Cys-Met-Arg-Thr-Cys-Gly-Gly-Ala (II)
The amino acid chain is cross-linked by three disulphide bridges formed between Cys(5) and Cys(55), Cys(14) and Cys(38) and Cys(30) and Cys(51), respectively.
The isoelectric point of aprotinin is quite high (approximately 10.5). This is mainly caused by a relatively high content of the positively charged amino acids lysine and arginine. The three-dimensional structure of the aprotinin molecule is very compact which makes it highly stable against denaturation at high temperatures, or by acids, alkalis or organic solvents, or against proteolytic degradation (cf. B. Kassell, Meth. Enzym. 19, 1970, pp. 844-852).
Aprotinin is known to inhibit various serine proteases, including trypsin, chymotrypsin, plasmin and kallikrein, and is used therapeutically in the treatment of acute pancreatitis, various states of shock syndrome, hyperfibrinolytic hemorrhage and myocardial infarction (cf., for instance, J. E. Trapnell et al, Brit. J. Surg. 61, 1974, p. 177; J. McMichan et al., Circulatory shock 9, 1982, p. 107; L .M. Auer et al., Acta Neurochir. 49, 1979, p. 207; G. Sher, Am. J. Obstet. Gynecol. 1977, p. 164; and B. Schneider, Artzneim. -Forsch. 26, 1976, p. 1606). Administration of aprotinin in high doses significantly reduces blood loss in connection with cardiac surgery, including cardiopulmonary bypass operations (cf., for instance, B. P. Bidstrup et al., J. Thorac. Cardiovasc. Surg. 97, 1989, pp. 364-372; W. van Oeveren et al., Ann. Thorac. Surg. 44, 1987, pp. 640-645).